CHAPTER 17 the base surge passing any point, in the sense that miltiplying d, ‘by the assumed decay rate, t™*'*, and then integrating from ty to ty gives the correct value of the total transit dose at the point. When integrated from t, to t,, the expression gives an idealized estimate of the dose-time history that smoothes out the effects of nonuniformity in the actual values of dy. Comparison of some results from Shot Wahoo with calculated values of dy, the maximum dose rate to be expected from airborne activity (the value of d at time ty) indicates that the calculated value of d; gives a close estimate of the maximum obeerved dose rate. Note that in thie model, the maximum dose rate occurs at ty; in the real case, the maxinnm dose rate occurs somewhat later. THE MODEL OF REFERENCE 48 A geometrical model of the bese surge is used as the source of raddation for the theoretical method of calculating transit radiation developed in Ref. 48. The geometrical and radiological parameters of the right circuler truncated cone used as the model depend on yield and purst depth, and the model is designed to be applicable to weapon yields from 1 KT to 100 KT. Surface and near-surface bursts are not covered. The geometries used are suggested by Photggraphic records of weapon tests and by theoretical scaling relationships;*’ but are adjusted to agree with radiological test data. Similarly, the radiological properties of the model, although guided by simplifying assumptions, are adjusted after comparison with weapon-test data. It is noted that this model takes into account only burst depth; water depth is not considered, although the development of Ref. 49 tacitly assumes shallow bursts are bottom bursts. It has been suggested thet the base-surge radii calculated for shallow bottom bursts are approximately valid for all shallow bursts, but recent data (from Operation Hydra IT)indicate that such an assumption is questionable. Numerical calculations required for prediction of dose rates and doses have been programmed for machine (IBM-704) computation at NRDL. A. Simplifying Assumptions The following simplifying assumptions were used in developing the model: 1. Air attenuation of radiation occurs but there is no attemiation by the water droplets that form the base surge. 2. Geamma-spectmm and buildup-factor calculations are replaced by use of an effective attenuation factor, © a substitution that takes into account absorption and scattering of gamma rays over the entire radiation pectrum. (Note that the effective attemation factor is different from an "average" or'effective" energy. ) 17-4] were er eee ee 49